This invention relates to techniques for material working including material deposition, reaction, and etching.
Techniques for metal deposition span nearly two centuries of scientific exploration beginning with the discovery of gold electroplating in the early nineteenth century to recent demonstrations of single crystal aluminum growth utilizing molecular beam epitaxy. Many of these techniques are described in a book entitled, Thin Film Technology, D. Van Nostrand Company, Inc., Princeton, N.J. (1968) by R. W. Berry, et al. They categorize metal deposition techniques into three broad categories:
(1) Chemical processes such as electrodeposition, chemical reduction, electroplating, and chemical vapor plating;
(2) Evaporation which is accomplished by using vacuum pumps to reduce the pressure inside a deposition chamber and then heating the metal to be evaporated in a filament or boat made of a high-melting point material. The heat is supplied typically by resistant heating, radio frequency induction, or electron bombardment. Molecular beam epitaxy deposition, mentioned above, falls within this genus; and
(3) Cathode sputtering which is similar to evaporation in that a partial vacuum is required but is dissimilar in that thermal energy is used in evaporation, whereas ion bombardment of the metal, causing ejection of electrons, is used for sputtering.
Both evaporation and sputtering have been practiced in the presence of a glow discharge as described by Berry et al., supra, pages 156-157 and 204-208. This variant of the evaporation technique has been termed "ion plating." Briefly, it entails establishing a glow discharge region between an evaporator filament and a cathode substrate. As the vapor atoms pass through the glow discharge, some are ionized and are accelerated to the substrate where metal deposition takes place.
Each of these prior art techniques, however, suffers from one or more of the following disadvantages: inefficiency in that relatively high currents produced slow deposition rates and thereby increase both processing time and the likelihood of contamination; the need for maintaining relatively high vacuums and the concomitant cost of equipment to do so; lack of precise control as to deposition time (hence layer thickness) and deposition direction (hence layer patterning); contamination when chemical solutions contact the workpiece or from boats used to carry the evaporant; and difficulty in depositing relatively high-melting point (low vapor pressure) metals.